Journal of Geotechnical and Geoenvironmental Engineering

The potential effects of soil liquefaction at level ground sites should be evaluated through examining soil element responses of the individual soil layers and system responses of the soil deposits they form. The cyclic responses and postliquefaction volumetric strain of uniform clean sand, sandy gravel, nonplastic silty sand, and nonplastic silt at the element level can be captured in a unified manner using relative density or the state parameter. The depositional environment should be characterized because geologic details, such as soil fabric, which can be discerned through detailed logging of high-quality continuous sampling, are important in evaluating liquefaction effects. Effective stress analysis enables soil system responses that govern the effects of liquefaction, including the formation of ejecta, to be investigated. A calibrated cone penetration test (CPT) procedure employing the liquefaction ejecta demand parameter captures key aspects of system response and provides an estimate of ejecta-induced building settlement. A probabilistic CPT-based procedure for estimating postliquefaction ground settlement is developed using laboratory and field case history databases. Correlations are developed to estimate $D_r$ or ${\psi }_o$ to enable use of the laboratory-based volumetric strain models. Adjustment factors enable the procedure to capture field observations of postliquefaction ground settlement. The proposed ground settlement procedure is combined with shear and ejecta-induced settlement procedures to estimate liquefaction-induced building settlement.

This paper explores the application of a numerical method for modeling pseudorandom cyclic loading, at very large cycle numbers, to the design of offshore wind turbine foundations. The work expands the development of a novel constitutive modeling framework, the hyper-plastic accelerated ratcheting model (HARM), for which the key constitutive equations and the calibration method are presented. HARM captures both the nonlinear hysteretic behavior during cycling and the accumulation of permanent deformation (ratcheting) with large cycle numbers in a rigorous, yet computationally efficient manner, enabling the computation of foundation response over a lifetime of loading. This paper demonstrates how the approach can be applied to the cyclic pile field testing from the pile soil analysis (PISA) project. Following calibration, the model is used to assess pile response to three load signals representative of operational and extreme loads throughout the lifetime of a full-scale wind turbine foundation: (1) a short storm, (2) a 35-h storm, and (3) lifetime loading. The paper discusses how computational efficiency can be achieved while maintaining a high level of calculation accuracy.

This paper presents the results of a series of load tests performed on a half-strip model footing (width $B=50\mathrm{mm}$) placed on the surface of samples prepared with one of two uniform silica sands [Ohio Gold Frac (OGF) sand and Ottawa 20–30 (OTC) sand] with different relative densities. The sand samples were air-pluviated inside a half-cylindrical calibration chamber equipped with imaging capabilities. Sequential, high-resolution images taken during the model footing load tests were analyzed using the digital image correlation (DIC) technique to obtain the displacement and strain fields in the sand domain. The effect of sand relative density on the footing load–settlement curves and bearing capacity factor $N_{\gamma }$ was investigated for both OGF and OTC sands. The results obtained from the model footing load tests show that, for a given relative density, the bearing capacity of the footing and the value of $N_{\gamma }$ decrease with increasing roundness of the sand particles; the effect of particle roundness on the value of $N_{\gamma }$ is more pronounced for dense sand than for loose sand. Different points on the footing load–settlement curve were identified to investigate the development of the collapse mechanism of the model footing. Plots of the maximum shear strain contours were shown to adequately capture shear localization in the sand domain during model footing loading. The thickness of the shear band was found to be on the order of $10D_{50}$ and $7D_{50}$ for the model footing tested on dense OGF and OTC sand samples, respectively.

The wind erosion resistance of the microbial-induced carbonate precipitation (MICP)-treated soil was investigated in this study using wind tunnel experiments. A wind tunnel was calibrated to simulate the atmospheric boundary layer (ABL). The erosion modes of the soil samples with increasing and cyclic wind loading were analyzed using digital imaging techniques. The calcium carbonate content and its uniformity in treated soils were determined using an atomic absorption spectrometer. The effect of soil relative density, soil type, MICP treatment protocol, and wind loads on wind erosion mitigation was evaluated. Based on the testing conditions, a MICP treatment protocol using 0.25 pore volume of bacteria medium (Sporosarcina pasteurii, ATCC 11859) followed by 0.25 pore volume of 0.3 M cementation medium was determined as the optimal treatment for increasing wind load resistance. A calcium content of 0.28% for the soil surface layer was the minimum calcium carbonate content necessary to mitigate wind erosion for the increasing wind loading condition. For the cyclic wind loading condition, a MICP treatment protocol to achieve a minimum calcium carbonate content of 0.68% was determined as the optimum treatment protocol.

Shake table experiments are conducted to assess the potential of the polymer injection technique as a liquefaction countermeasure. A large 2.9 m high (10 ft) laminar soil container on a $3.9\times 1.85\mathrm{m}$ ($13\times 6\mathrm{ft}$) shake table is employed. Mitigation of liquefaction-induced settlement for a shallow foundation is explored. In a series of two shake table experiments, the system response is studied first without (baseline) and subsequently with polymer injected into the liquefiable stratum. Each test is densely instrumented to provide insights into the dynamic response of the soil and foundation system. Furthermore, cone penetration tests (CPTs) are performed pre- and postinjection to assess the extent of soil improvement. Strong base excitation is imparted by the shake table, resulting in liquefaction and excessive foundation settlement in the original baseline test. In the second test, with the polymer injection countermeasure, a significant reduction is observed in the tendency for liquefaction and the resulting foundation settlement. After this test, careful excavation provided additional insights into the polymer’s configuration within the deposit, increasing overall soil relative density, confinement and creating solidified paths for the shallow foundation load toward the lower, more competent stratum. As such, these mechanisms have the potential to allow for: (1) an increase in soil resistance to liquefaction, and (2) a significant reduction in settlement of overlying shallow foundations.

Despite the clearly stated procedures in current standards, and contrary to its name, nonstandard execution of the standard penetration test (SPT) has been common. The use of different equipment and procedures produces significantly different SPT blow counts. To minimize the effects of these differences, correction factors are applied. Two of these corrections factors, namely hammer energy efficiency ratio ($C_E$) and rod length ($C_R$) corrections, are the scope of this research study. With the intent of quantifying the effects of variabilities and reducing the uncertainties, SPT hammer efficiency measurements were compiled from available literature. Additionally, new hammer energy measurements were performed in the field, controlling the variables of the problem. The resulting database is used to probabilistically develop a set of new $C_E$ and $C_R$ recommendations. The recommended mean energy ratios for safety hammer and automatic hammers are estimated as $67\%\pm 11\%$ and $78\%\pm 12\%$, respectively, which are higher than typically assumed values in engineering practice. The recommended rod length correction values at shallow depths, proven to be also a function of SPT blowcounts, N ($\mathrm{SPT}\text{-}N$) values, are higher than typically used values. This suggests less pronounced rod length effects. Additionally, a modified procedure to assess the stress-wave energy at anvil and above the SPT sampler elevations is introduced.

A soil’s hydraulic conductivity is a highly nonlinear function of water content, decreasing many orders of magnitude from its saturated state to dry state. This nonlinearity is a macroscopic manifestation of microscopic soil properties of pore structure, pore connectivity, and mineral–water interaction. These microscopic soil properties are underpinned by two distinct soil–water interaction mechanisms: adsorption and capillarity. Herein, a soil hydraulic conductivity equation was developed by incorporating capillary pore flow and adsorptive film flow. The capillary pore flow is captured via a model of bundle of cylindrical capillaries, whereas the adsorptive film flow is established using a film thickness function incorporating adsorption mechanisms of the electric double layer, van der Waals, surface hydration, and cation hydration potentials. The transition between adsorptive film flow and capillary flow is delineated by a water cavitation probability function. The proposed soil hydraulic conductivity equation automatically can fulfill the five necessary physical constraints imposed by underlying soil–water interaction characteristics. The proposed hydraulic conductivity equation can capture the hydraulic conductivity data very well for a wide array of soils, and outperforms several established soil hydraulic models in full matric potential ranges, especially in the low matric potential range in which adsorptive film flow is dominant.

The use of prefabricated horizontal drains (PHDs) with combined surcharge and vacuum preloading is an effective improvement approach for dredged clayey slurries. However, there is no large-strain analysis method for PHD-induced consolidation of high-water-content sludge, even though it is a typical large-strain problem. This study develops a two-dimensional plane strain model based on Gibson’s large-strain theory, considering horizontal and vertical flows, nonlinear hydraulic conductivity, and compressibility during the consolidation process. The alternative direction implicit (ADI) difference method is used to solve the governing equation. The proposed model is verified by the data from an analytical one-dimensional (1D) large-strain model and from field measurements. Compared with the improved small-strain models, the proposed model produces a slower consolidation of sludge. Furthermore, the analyses incorporating geometrical and mechanical nonlinearities show that, in comparison with the external load and the horizontal permeability, the spacing of the PHDs (horizontal and vertical) and the vertical permeability are more crucial factors significantly impacting consolidation efficiency. Specifically, smaller PHD spacing and greater vertical permeability lead to a more efficient consolidation.

Design codes vary in their recommendations for the end-bearing response for bored piles founded in sand, both for the ultimate design value and the response at small settlements. The ultimate end-bearing resistance may be expressed either in terms of bearing factors $N_q$ relative to the in situ vertical effective stress, with the $N_q$ value varying with the friction angle of the sand, or as a factor applied to in situ test data, such as the standard penetration test blow count or the tip resistance $q_c$. Numerical studies have led to proposed ratios of design end-bearing pressure to $q_c$ at specific settlement ratios, such as 5% and 10% of the pile diameter. The work presented here used numerical analysis to evaluate the full pile base response from initial stiffness to ultimate end-bearing resistance at a settlement ratio of 10% of the pile diameter. The resulting base responses are suitable for implementation in beam column analyses and have been validated by comparison with published design guidelines and with data from a full-scale instrumented pile load test.

The pore pressure model was developed in the past to predict liquefaction induced by an earthquake. Its main advantage is that its parameters can be obtained from experiments based on direct measurement of pore pressure data. However, two downsides of the pioneering model are that its parameters are distinct for each relative density, and that liquefaction curves derived from the model have not been evaluated fully based on well-known triggering liquefaction curves. This research advances the pore pressure model by introducing a method of adjusting the incremental pore pressure rise using calibration factors. Based on the behavior of clean sand, calibration factors, which take into account the effect of the critical stress ratio, earthquake magnitude, and initial stress level, were derived. The calibrated pore pressure model was compared with data from direct simple shear tests to verify the derived calibration factors, and good agreement between the measured and predicted data was observed.

Leachate, consisting of organic acids such as acetic acid (AA) and oxalic acid (OA), commonly is released into groundwater from municipal solid waste dumps and uncontrolled landfills. Slurry trench cutoff walls commonly are used to contain such contaminated groundwater, thereby protect the surrounding public and the environment. However, no studies have assessed comprehensively the effects of organic acid–laden groundwater exposure on the hydraulic conductivity and microscopic characteristics of sand–bentonite (SB) backfill in the cutoff walls. Several series of free swell, liquid limit, and flexible-wall hydraulic conductivity tests were conducted to quantify the effects of AA and OA exposure on the free swell index of bentonite and hydraulic conductivity and liquid limit of SB backfill. Results showed that the free swell index of bentonite and the liquid limit of SB backfill decreased with increasing concentrations of AA and OA. Exposure to AA yielded a lower free swell index of bentonite and liquid limit of SB backfill than those of OA with the same concentration. Increasing concentrations of AA and OA resulted in an increase in the hydraulic conductivity of SB backfills. Exposure to AA yielded higher hydraulic conductivity of SB backfill than OA with the same concentration. Mechanisms for increased hydraulic conductivity under organic acid exposure were ascertained based on the microstructure and compositional changes quantified by field-emission scanning electron microscopy (FESEM), mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), X-ray fluorescence (XRF), cation exchange capacity (CEC), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR) analyses.

Liquid addition to landfilled municipal solid waste (MSW) is a practice employed to accelerate the biodegradation of the organic fraction of MSW and ensuing gas generation. Pore landfill gas (LFG) and leachate pressure from the added moisture and enhanced gas generation are expected to impact the geotechnical stability of landfill slopes. The impact of moisture addition and gas collection on the stability of landfills was numerically modeled using transient isothermal dual-phase flow and slope stability modeling. The temporal variation in the factor of safety (FS) for slope stability analysis was estimated for the simultaneous flow of LFG and leachate with and without gas collection and leachate recirculation for varying LFG generation rates and waste moisture contents. A significant decline in the FS for landfill slope stability was observed when recirculating leachate without active gas collection. Even without pressurized leachate recirculation, a significant decline in the FS value was observed for landfills with relatively high in situ moisture content without active gas collection. In some modeled scenarios without LFG collection, the FS value was lower than 1. The analysis suggests that the landfill side slope stability analysis should incorporate LFG generation and the resultant pressure for landfills containing high-moisture-content waste and for the landfill with pressurized leachate recirculation. The analysis suggests that an efficient gas collection system plays a critical role in the geotechnical stability of the slope of wet landfills and the performance of leachate recirculation trenches.

Clay embankments used for road, rail, and flood defense infrastructure experience a suite of weather-driven deterioration processes that lead to a progressive loss of hydromechanical performance: micro-scale deformation (e.g., aggregation and desiccation), changes in soil-water retention, loss of strength, and macro-scale deformation. The objective of this study was to develop a numerical modeling approach to simulate the construction and long-term, weather-driven hydromechanical behavior of clay embankments. Subroutines within a numerical modeling package were developed to capture deterioration processes: (1) strength reduction due to wet-dry cycles; (2) bimodality of the near-surface hydraulic behavior; (3) soil-water and soil-gas retentivity functions considering void ratio dependency; and (4) hydraulic and gas conductivity functions considering void ratio dependency. Uniquely, the modeling approach was comprehensively validated using laboratory tests and nine years of field measurements from a full-scale embankment. The modeling approach captured the variation of near-surface soil moisture and matric suction over the monitored period in response to weather cycles. Further, the developed model approach could successfully simulate weather-driven deterioration processes in clay embankments. The model predictions manifested the ability of the modeling approach in capturing deterioration features such as irrecoverable increases in void ratio and hydraulic permeability near surface. The developed and validated numerical modeling approach enables forecasting the long-term performance of clay embankments under a range of projected climate conditions.

This paper presents a novel approach to smoothen the abrupt stiffness variation along railway transitions and provides a step-by-step design of a multistep transition zone comprising adjoining segments with changing stiffness values. The influence of stiffness on track dynamic response applied to transition zones is investigated analytically, considering a beam on an elastic foundation. Vertical track displacements for varying stiffness values under different combinations of axle loads and speeds are calculated analytically and numerically, and they are found to be in good agreement. The results indicate that stiffer tracks undergo less settlement compared to those having a smaller stiffness. The effect of abrupt stiffness variation at transition sections is analyzed under four-carriage loading that causes considerable differential settlement, which is further exacerbated by increased train speeds. A mathematical process is introduced to determine the optimum stiffness of each segment to ensure a gradual change in stiffness while minimizing the corresponding differential settlement. The proposed methodology is further validated through the finite element modelling approach and worked-out examples epitomizing the effects of stiffness variation along the number of transition steps. From a practical perspective, this study provides a significant extension for design rejuvenation of transition zones by minimizing the differential settlement at any two consecutive transition segments.

This research analyzed the role of footing aspect ratio in influencing the limit bearing capacity and associated failure mechanism in saturated, structured clays. The effects of footing aspect ratio and footing–soil interface conditions on the extent of soil destructuration, during mobilization of limit load, were investigated using advanced finite-element analyses. These analyses employed a clay constitutive model that accounted for continuous load-induced evolutions of soil destructuration and stress-induced anisotropy. The soil destructuration process caused 30%–35% reduction in the limit bearing capacity of shallow foundations. Moreover, the proposed analysis-based shape factor for footings in structured clay suggests that the use of shape factors available in the literature would overpredict the limit bearing capacity for footings in clays prone to destructuration.